Liquid crystal composition

ABSTRACT

The present invention relates to a liquid crystal composition used for thermal writing type liquid crystal display devices utilizing a thermooptical effect, and a liquid crystal display element using the composition. 
     The object of the present invention is to provide a liquid crystal composition having an extremely narrow nematic range and a low-melting phase transition point, and also to provide a liquid crystal display element using the composition. 
     The present invention is directed to a liquid crystal composition mainly comprising a component A comprising 4-n-octyl-4&#39;-cyanobiphenyl, 4-n-dodecyl-4&#39;-cyanobiphenyl and at least one member of 4-n-alkyl-4&#39;-cyanobiphenyls represented by the formula (I), ##STR1## wherein R 1  is an alkyl group of 9, 10 or 11 carbon atoms, and a component B comprising at least one member of 4-n-alkanolyloxy-4&#39;-cyanobiphenyls represented by the formula (II) ##STR2## wherein R 2  is an alkyl group of 8 or 9 carbon atoms, and at least one member of 4-n-alkanoyloxy-4&#39;-cyanobiphenyls represented by the formula (III) ##STR3## wherein R 3  is an alkyl group of 10, 11 or 12 carbon atoms, the ratio of the component A to the component B being in the range of 95:5 to 45:55. 
     The liquid crystals composition may further comprise at least one member of 4-n-alkoxy-4&#39;-cyanobiphenyls represented by the formula (IV) ##STR4## wherein R 4  is an alkyl group of 8 to 12 carbon atoms.

INDUSTRIAL FIELD

The present invention relates to a liquid crystal composition used forliquid crystal display devices of a thermally addressing type utilizinga thermooptical effect, and this liquid crystal composition ischaracterized by having an extremely narrow nematic phase and alsohaving a low-melting smectic phase.

BACKGROUND ART

In recent years, the development of liquid crystal display elements isremarkable, and these display elements are mostly directed to theapplication of nematic liquid crystals. On the other hand, liquidcrystal displays of different driving modes, utilizing characteristicsof other liquid crystal phases have also been intensively researched forpractical use, and as one of these devices, there is a thermal writingprojection device utilizing a thermooptical effect of a smectic A phase.The mode of such a device can provide a display of a far larger area anda far higher capacity in the number of figures, as compared with aconventional TN mode (twisted nematic mode).

Characteristics required for the liquid crystal materials used in thisfield include the following:

(1) a wide smectic A phase range (preferably, a smectic A phase rangedown to 0° to -20° C.),

(2) an extremely narrow nematic phase range,

(3) a high birefringence index,

(4) a small specific heat and a low phase transition energy; and

(5) a large dielectric anisotropy value.

Of these requirements, the items (1), (2) and (3) are considered to beimportant for improving the quality level of display such as contrast ona projected screen. As to liquid crystal materials having theabove-mentioned characteristics, no single compound has yet been found,and hence mixtures of various liquid crystal compounds have now beeninvestigated. Examples of these liquid crystal compounds can berepresented by the following general formulae: ##STR5##

Furthermore, examples of compositions of these compounds are set forthin Table 1.

                  TABLE 1                                                         ______________________________________                                        Compo-               mp      SN    NI    NR                                   sition  Compounds    (°C.)                                                                          (°C.)                                                                        (°C.)                                                                        (°C.)                         ______________________________________                                        a       I.sub.8, I.sub.10, I.sub.15                                                                24      73.5  74    0.5                                  b       II.sub.8, II.sub.10                                                                        12      37    42    5                                    c       II.sub.8, II.sub.10, V.sub.8                                                                6      53    56    3                                    d       II.sub.8, II.sub.10, IV.sub.9                                                               8      41.5  47    5.5                                  e       II.sub.8, III.sub.10, IV.sub.9                                                             -30     46.8    51.0                                                                              3.2                                  f       II.sub.8, II.sub.10, III.sub.10                                                            -32.7   54.7    57.3                                                                              2.6                                          III.sub.12, IV.sub.9, VI.sub.8                                        ______________________________________                                    

In Table 1, the respective abbreviations have the following meanings:

mp: Melting point (°C.)

SN: Smectic/nematic transition point (°C.)

NI: Nematic/isotropic transition point (°C.)

NR: Nematic range (°C.)

[=NI point (°C.)--SN point (°C.)]

In the column labelled "Compound" in the table, for example, I₈ meansthe compound of n=8 of Formula (I), mentioned above.

With regard to the composition a, the nematic range is as extremelynarrow as 0.5° C., but the melting point is as high as 24° C., which isin the vicinity of room temperature. Therefore, this composition isdifficult for practical use, though it seems to be usable inexperiments. On the other hand, with regard to the compositions e and f,the melting points are as low as -30° C. and -32.7° C., respectively,but the nematic ranges are as wide as 3.2° C. and 2.6° C., respectively.Thus these compositions are not always satisfactory.

The nematic range is a factor which has an influence on the writing rateand the display contrast of the display elements, and when the nematicrange is wide, the writing rate is low and the contrast also isinferior. That is, when thermal writing is carried out within a widenematic range, a long cooling time is required in the nematic phase inthe step of forming an opaque smectic phase from an isotropic liquid viaa nematic phase, which constitutes a factor of retarding the writingrate. Furthermore, when the nematic phase state remains for a longperiod of time, the liquid crystal is oriented by a substrate subjectedto an orientation treatment (vertical orientation or homogeneousorientation), so that no scattered smectic A phase can be obtained,which constitutes a factor in deteriorating the contrast.

With regard to the melting point, if it is 0° C. or lower, thecompositions are considered to be suitable for typical uses. Because thethermal writing type liquid crystal device is used indoors, it can beconsidered that the device is usually not used in an environment of 0°C. or lower.

In addition to the above-mentioned compositions, the other thermalwriting liquid crystal compositions are disclosed in Japanese PatentApplication Laid-open Publication Nos. 144383/1985, 252686/1985,268790/1986, etc. but compositions having a nematic range of 2° C. orlower and at the same time a melting point of 0° C. or lower have notyet been found.

The object of the present invention is to provide a liquid crystalcomposition for thermal writing liquid crystal device elements, and aliquid crystal display element using the composition, and morespecifically, a liquid crystal composition having characteristics of anextremely narrow nematic range and a low-melting phase transition point,and a thermal writing liquid crystal device element using thecomposition.

DISCLOSURE OF INVENTION

The present inventors have made intensive research in order to solve theabove-mentioned problems of the prior art, and as a result have obtaineda liquid crystal composition having a nematic range of 2° C. or lowerand a melting point of 0° C. or lower. Thus, the present invention hasbeen accomplished.

The first specific feature of the present invention is directed to aliquid crystal composition mainly comprising a component A comprising4-n-octyl-4'-cyanobiphenyl, 4-n-dodecyl-4'-cyanobiphenyl and at leastone member of 4-n-alkyl-4'-cyanobiphenyls represented by the formula (I)##STR6## wherein R¹ is an alkyl group of 9, 10 or 11 carbon atoms, and acomponent B comprising at least one member of4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II)##STR7## wherein R² is an alkyl group of 8 or 9 carbon atoms, and atleast one member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented by theformula (III) ##STR8## wherein R³ is an alkyl group of 10, 11 or 12carbon atoms, the ratio of the component A to the component B being inthe range of 95:5 to 45:55.

Furthermore, another specific feature of the present invention isdirected to a liquid crystal composition according to theabove-mentioned composition, further comprising as a component C, atleast one member of 4-n-alkoxy-4'-cyanobiphenyls represented by theformula (IV) ##STR9## wherein R⁴ is an alkyl group of 8 to 12 carbonatoms.

In the component A of the liquid crystal composition according to thepresent invention, a weight ratio of 4-n-octyl-4'-cyanobiphenyl to4-n-dodecyl-4'-cyanobiphenyl is in the range of 1:1 to 9:1, preferably3:2 to 4:1. Furthermore, concrete examples of the4-n-alkyl-4'-cyanobiphenyls represented by the formula (I) are (a)4-n-nonyl-4'-cyanobiphenyl, (b) 4-n-decyl-4'-cyanobiphenyl and (c)4-n-undecyl-4'-cyanobiphenyl. In the component A,4-n-octyl-4'-cyanobiphenyl and 4-n-dodecyl-4'-cyanobiphenyl arecontained in an amount of 40% or more. Preferably, the compounds of theformula (I) are used in the form of a mixture of the above-mentionedcompounds (a), (b) and/or (c), and the weight ratio of the compound (a)to the compound (b}and/or (c) is preferably in the range of 7:3 to 3:7,more preferably about 1:1.

In the component B of the liquid crystal composition according to thepresent invention, the ratio of at least one member of the4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II) to atleast one member of the 4-n-alkanoyloxy-4'-cyanobiphenyls represented bythe formula (III) is in the range of 55:45 to 95:5.

Moreover, the ratio of the component A to the component B whichconstitute the liquid crystal composition of the present invention is inthe range of 95:5 to 45:55. When the content of the component B is morethan 55%, the melting point of the composition is high, and when it isless than 5%, the effect of lowering the melting point is insufficientand the influence on NR is also slight.

The component C of the liquid crystal composition of the presentinvention is at least one member of the 4-n-alkoxy-4'-cyanobiphenylsrepresented by the formula (IV), but it is preferred that two or more ofthese compounds be used. The amount of the component C used is 25% orless, preferably 20% or less, of the total weight of the composition.When it exceeds 25%, the melting point of the composition, etc. areadversely affected.

The second specific feature of the present invention is directed to aliquid crystal display element for thermal writing characterized byusing a liquid crystal composition which contains a component Acomprising 4-n-octyl-4'-cyanobiphenyl, 4-n-dodecyl-4'-cyanobiphenyl andat least one member of 4-n-alkyl-4'-cyanobiphenyls represented by theformula (I) ##STR10## wherein R¹ is an alkyl group of 9, 10 or 11 carbonatoms, and a component B comprising at least one member of4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II)##STR11## wherein R² is an alkyl group of 8 or 9 carbon atoms, and atleast one member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented by theformula (III) ##STR12## wherein R³ is an alkyl group of 10, 11 or 12carbon atoms, the ratio of the component A to the component B being inthe range of 95:5 to 45:55.

Furthermore, another specific feature of the present invention isdirected to a liquid crystal element for thermal writing characterizedusing a liquid crystal composition in which the components A and Bfurther contain, as a component C, at least one member of4-n-alkoxy-4'-cyanobiphenyls represented by the formula (IV) ##STR13##wherein R⁴ is an alkyl group of 8 to 12 carbon atoms.

The liquid crystal composition of the present invention can be usedtogether with a dye, a cholesteric liquid crystal and a high-temperatureliquid crystal used for the adjustment of the NI point, etc.

As the dye, there can be employed a dichroic dye in a visible regionwhich aims at improving color display or contrast, or a dichroic dyeabsorb energy of the wave length of laser beams, which dyes are used toadsorb the energy of laser beams and thereby improve the thermalefficiency. Such dichroic dyes may be those used for guest/host ofliquid crystals. Typical examples of such dyes include azo dyes,anthraquinone dyes and squalirium dyes.

The content of the dye is 10% or less and usually 5% or less.

Typical examples of the cholesteric liquid crystal include4'-cyano-4-(2'-methylbutyloxy)biphenyl,4'-cyano-4-(2'-methylbutyl)biphenyl, 4'-(2-methylbutyloxy)benzoicacid-4'-cyanophenyl,2-chloro-1,4-bis(4'-2-methylbutyloxybenzoyloxy)benzene,4'-(2-methylbutyl)-4-biphenylcarboxylic acid-4'-pentylcyclohexyl ester.The content of the cholesteric liquid crystal is 30% or less and usually20% or less.

Typical examples of the high-temperature liquid crystal include4-n-nonyl-4"-cyanoterphenyl, 4-n-nonyloxy-4"-cyanoterphenyl,4-(trans-4-n-nonylcyclohexyl)-4'-cyanobiphenyl,1-(4'-n-hexylphenyl)-2-(4'-cyano-4-biphenyl)ethane,trans-4-n-nonylcyclohexanecarboxylic acid-4'-cyanobiphenyl ester,1-(4'-n-hexylcyclohexyl)-2-(4'-cyano-4-biphenyl)ethane,trans-4-n-nonylbenzoic acid-4'-cyano-4-biphenyl ester andtrans-4-n-nonyloxybenzoic acid-4'-cyano-4-biphenyl ester. The content ofthe high-temperature liquid crystal is 30% or less, and preferably 20%or less.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail with reference tothe following examples, but the scope of the present invention shouldnot be limited to these examples.

EXAMPLES 1 TO 7

Liquid crystal compositions were prepared in accordance withpredetermined proportions (% by weight) shown in Table 2, and theircharacteristics were then measured. The results are set forth in thesame table.

COMPARATIVE EXAMPLES 1 to 9

Following the same procedure as in Examples 1 to 7 liquid crystalcompositions were prepared, and their characteristics were thenmeasured. The results are set forth in Table 3.

                                      TABLE 2                                     __________________________________________________________________________                                      Example                                     Component                                                                           Formula                                                                            Compound               1  2  3  4  5  6  7                         __________________________________________________________________________    A          4-n-octyl-4'-cyano-    28 50.4                                                                             53.2                                                                             35.3                                                                             35.3                                                                             47.9                                                                             29.4                                 biphenyl                                                           A          4-n-dodecyl-4'-cyano-  7.0                                                                              12.6                                                                             13.3                                                                             15.1                                                                             8.8                                                                              12.0                                                                             7.3                                  biphenyl                                                           A     I                                                                                   ##STR14##             7.5                                                                              13.5                                                                             14.3                                                                             10.8                                                                             9.5                                                                              12.8                                                                             12.2                      A     I                                                                                   ##STR15##             7.5                                                                              13.5                                                                             14.3                                                                             10.8                                                                             9.4                                                                              12.8                                                                             12.2                      B     II                                                                                  ##STR16##             17.5                                                                             3.5                                                                              1.8                                                                              12.6                                                                             9.0                                                                              1.6                                                                              18.8                      B     II                                                                                  ##STR17##             24.4                                                                             4.9                                                                              2.4                                                                              8.4                                                                              15.7                                                                             2.2                          B     III                                                                                 ##STR18##                      2.8                                B     III                                                                                 ##STR19##             8.1                                                                              1.6                                                                              0.8                                                                              4.2                                                                              5.3                                                                              0.7                                                                              7.5                       C     IV                                                                                  ##STR20##                         5.6                                                                              5  12.6                      C     IV                                                                                  ##STR21##                         1.4                                                                              5                            __________________________________________________________________________    The numeral values in the table denot the proportions (%) of the              respective                                                                    components.                                                                   __________________________________________________________________________    cp (°C.)                   60.0                                                                             46.2                                                                             46.2                                                                             54.1                                                                             57.1                                                                             50.2                                                                             57.8                      SN point (°C.)             59.1                                                                             44.5                                                                             44.3                                                                             53.8                                                                             56.3                                                                             48.6                                                                             56.3                      NR (°C.)                   0.9                                                                              1.7                                                                              1.9                                                                              0.3                                                                              0.8                                                                              1.6                                                                              1.5                       Melt Starting Point (°C.)  -9 -27                                                                              -12                                                                              -17                                                                              -20                                                                              -24                          Melt Ending Point (°C.)    -3 -24                                                                              -3 -11                                                                              -10                                                                              -9 -16                       __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                                        Comparative Example                       Component                                                                            Formula                                                                            Compound                1  2  3  4  5  6  7  8  9                 __________________________________________________________________________    H           4-n-octyl-4'-cyano-     56    22.4     50.4                                                                             57.9  60                            biphenyl                                                          A           4-n-dodecyl-4'-cyano-   14    5.6      12.6     40                            biphenyl                                                          A      I                                                                                   ##STR22##              15    6.0      13.5                       A      I                                                                                   ##STR23##              15    6.0      13.5                                                                             17.1                    B      II                                                                                  ##STR24##                 35.0                                                                             21.0                                                                             30                               B      II                                                                                  ##STR25##                 48.8                                                                             29.3                                                                             52.5     25.0                    B      III                                                                                 ##STR26##                                                        B      III                                                                                 ##STR27##                 16.2                                                                             9.8                                                                              17.5                             C      IV                                                                                  ##STR28##                          80 8.0   50                   C      IV                                                                                  ##STR29##                          20 2.0   50                   __________________________________________________________________________    The numeral values in the table denote the proportions (%) of the             respective                                                                    components.                                                                   __________________________________________________________________________    cp (°C.)                     44.7                                                                             78.1  78.7                                                                             80.5                                                                             47.8                                                                             50.4                                                                             82.3                                                                             46.2              SN point (°C.)               42.7                                                                             76.4  77.4                                                                             74.2                                                                             45.0                                                                             47.4                                                                             none                                                                             45.8              NR (°C.)                     2.0                                                                              1.7   1.3                                                                              6.3                                                                              2.8                                                                              3.0   0.4               Melt Starting Point (°C.)    -8 18 -4 18 31 -16                                                                              -22                                                                              43.6                                                                              7                Melt Ending Point (°C.)       0 21  3 30 43 -3 -14                                                                              51.3                                                                             21                __________________________________________________________________________

INDUSTRIAL USAGE

The liquid crystal composition and the liquid crystal element of thepresent invention are characterized by having an extremely narrownematic phase temperature range and a low-melting phase transitionpoint, and therefore they are suitable to use for thermal writing liquidcrystal displays.

In the liquid crystal composition of the present invention, a nematicrange can be actually set to a level of 2° C. or lower, and thus awriting rate of the display element can be accelerated. In addition, thecontrast on a projection screen is good, whereby display quality levelcan be improved remarkably. Since the composition has a melting point of0° C. or lower, the liquid crystal composition of the present inventioncan be used for thermal writing type liquid crystal displays without anyproblems even when utilized indoors and at room temperature. Thus, theliquid crystal composition is a practically usable liquid crystalmaterial.

We claim:
 1. A liquid crystal composition having a nematic range of nomore than 2 C° and a melting point of no higher than 0° C., saidcomposition mainly comprising a component A including4-n-octyl-4'-cyanobiphenyl, 4-n-dodecyl-4'-cyanobiphenyl and at leastone member of 4-n-alkyl-4'-cyanobiphenyls represented by the formula (I)##STR30## wherein R¹ is an alkyl group of 9, 10 or 11 carbon atoms, anda component B comprising at least one member of4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II)##STR31## wherein R² is an alkyl group of 8 or 9 carbon atoms, at leastone member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented by theformula (III) ##STR32## wherein R³ is an alkyl group of 10, 11 or 12carbon atoms, the ratio of the component A to the component B being inthe range of 95:5 to 45:55.
 2. A liquid crystal composition according toclaim 1 further comprising at least one member of4-n-alkoxy-4'-cyanobiphenyls represented by the formula (IV) ##STR33##wherein R⁴ is an alkyl group of 8 to 12 carbon atoms.
 3. A liquidcrystal composition according to claim 1 wherein the ratio of4-n-octyl-4'-cyanobiphenyl to 4-n-dodecyl-4'-cyanobiphenyl is in therange of 1:1 to 9:1; both of these compounds are contained in an amountof 40% or more in the component A; and the ratio of at least one memberof 4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II) toat least one member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented bythe formula (III) is in the range of 55:45 to 95:5.
 4. A liquid crystalcomposition according to claim 1 including compounds of formula (I)wherein R¹ comprises alkyl groups having 9 and 10 carbon atoms;compounds of formula (II) wherein R² comprises alkyl groups having 8 and9 carbon atoms and compounds of formula (III) wherein R³ comprises alkylgroups having 11 and 12 carbon atoms.
 5. A liquid crystal compositionaccording to claim 2 wherein the ratio of 4-n-octyl-4'-cyanobiphenyl to4-n-dodecyl-4'-cyanobiphenyl is in the range of 1:1 to 9:1; both ofthese compounds are contained in an amount of 40% or more in thecomponent A; and the ratio of at least one member of4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II) to atleast one member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented by theformula (III) is in the range of 55:45 to 95:5.
 6. A liquid crystalcomposition according to claim 2 including compounds of formula (I)wherein R¹ comprises alkyl groups having 9 and 10 carbon atoms;compounds of formula (II) wherein R² comprises alkyl groups having 8 and9 carbon atoms; compounds of formula (III) wherein R³ comprises an alkylgroup having 12 carbon atoms; and compounds of formula (IV) wherein R⁴comprises alkyl groups having 8 and 12 carbon atoms.
 7. A liquid crystaldisplay element for thermal writing including a liquid crystalcomposition having a nematic range of no more than 2 C° and a meltingpoint of no higher than 0° C., mainly comprising a component A including4-n-octyl-4'-cyanobiphenyl, 4-n-dodecyl-4'-cyanobiphenyl and at leastone member of 4-n-alkyl-4'-cyanobiphenyls represented by the formula (I)##STR34## wherein R¹ is an alkyl group of 9, 10 or 11 carbon atoms, anda component B comprising at least one member of4-n-alkanoyloxy-4'-cyanobiphenyls represented by the formula (II)##STR35## wherein R² is an alkyl group of 8 or 9 carbon atoms, and atleast one member of 4-n-alkanoyloxy-4'-cyanobiphenyls represented by theformula (III) ##STR36## wherein R³ is an alkyl group of 10, 11 or 12carbon atoms, the ratio of the component A to the component B being inthe range of 95:5 to 45:55.
 8. A liquid crystal display element forthermal writing including a liquid crystal composition according toclaim 7, further comprising at least one member of4-n-alkoxy-4'-cyanobiphenyls represented by the formula (IV) ##STR37##wherein R⁴ is an alkyl group of 8 to 12 carbon atoms.
 9. A liquidcrystal display element for thermal writing according to claim 8including compounds of formula (I) wherein R¹ comprises alkyl groupshaving 9 and 10 carbon atoms; compounds of formula (II) wherein R²comprises alkyl groups having 8 and 9 carbon atoms; compounds of formula(III) wherein R³ comprises an alkyl group having 12 carbon atoms; andcompounds of formula (IV) wherein R⁴ comprises alkyl groups having 8 and12 carbon atoms.